This invention relates to an improved brush device in a rotary electric machine such as a starter motor.
FIG. 3 is a plan view showing a conventional brush device in the rotary electric machine. In FIG. 3, a brush holding frame 1 is molded of a thermosetting synthetic resin. The brush holding frame 1 has brush holding portions 1a and 1b each of which holds a plus brush 2a or a minus brush 2b. Brush springs 3 are provided within the brush holding portions 1a and 1b. The brush springs 3 urge the brushes 2a and 2b against a commutator 4 so that a tip end of each brush is attached to the commutator 4. In addition, protruding portions 5a and 5b are formed integrally with the brush holding frame 1. Mounting pieces 6a and 6b made of metal are slidably engaged with protruding portions 5a and 5b, respectively. The mounting piece 6a is connected to lead wires 7a connected to minus brushes 2a through a protruding piece 8. In the same way, the mounting piece 6b is connected to lead wires 7b connected to the plus brush 2b. Further, a lead wire 9 is connected at one end to the mounting piece 6b and at the other end to a terminal 10. An insulative plate 11 is used for insulating between the brush holding frame 1 and a rear bracket (not shown). The insulative plate 11 is provided so as to cover substantially all the side walls of the brush holding frame 1.
In the conventional brush device thus constructed, the mounting pieces 6a and 6b which are slidably engaged with protruding portions 5a and 5b are fixed to the rear bracket and are accommodated in the rear bracket. In addition, the mounting piece 6a on the minus side is grounded through the metal rear bracket and the terminal 10 on the plus side is connected to a positive terminal of an electromagnetic switch (not shown).
According to the conventional brush device in rotary electric machine is constructed as described above. When the brush holding frame 1 is installed as a starter motor, the brash holding frame 1 is accommodated in the rear bracket. Therefore, an outer diameter of the brush holding frame 1 and hence a length of brush holding portions 1a and 1b is limited. As a result, there are problems that it is impossible to elongate the length of brushes 2a and 2b so that the service life of brushes 2a and 2b are short. In addition, since the brush holding frame 1 and rear bracket are, respectively, constituted as separate components, there are problems that the conventional brush device becomes heavy in weight with an increased cost.